Standard mineral spirits used in making typical interior and exterior paint formulations normally contain about 20 percent aromatic compounds. For various reasons, including environmental and ecological concerns, there is a current demand for paint resins that are soluble in paraffinic solvents which do not contain aromatic compounds. However, it is also important for the resin used in such applications to maintain a high level of hardness and ultra-violet light resistance. This desirable combination of properties has heretofore been elusive. More specifically, in the past it has only been possible to improve solubility in paraffinic solvents by compromising hardness and/or ultra-violet light (UV) resistance.
U.S. Pat. Nos. 5,496,905 and 5,504,143 disclose a resin for paints which is highly soluble in paraffinic solvents and which has good resistant to ultra-violet light. These resins contain from about 10 weight percent to about 55 weight percent para-tertiary-butyl styrene (PTBS). These resins also contain about 20 weight percent to about 80 weight percent of at least one alkyl methacrylate monomer, from about 2 weight percent to about 25 weight percent alkyl acrylate monomer, and optionally up to about 40 weight percent of a vinyl aromatic monomer in addition to the PTBS. However, despite the fact that the resin described in U.S. Pat. Nos. 5,496,905 and 5,504,143 has good resistance to ultra-violet light coatings made therewith tend to yellow and discolor over time with exposure to ultra-violet light.
This invention disclose a resin for paints which is highly soluble in paraffinic solvents and which has excellent resistance to ultra-violet light. Coatings made with these resins are highly resistant to yellowing and discoloration on exposure to ultra-violet light over long periods of time. These resins are comprised of repeat units which are derived from (a) about 5 to about 60 weight percent tertiary-butyl cyclohexyl methacrylate, (b) 0 to about 40 weight percent vinyl aromatic monomers, (c) about 20 to about 80 weight percent alkyl methacrylate monomers, and (d) about 1 to about 30 weight percent alkyl acrylate monomers.
This invention more specifically discloses a resin which is particularly useful in making paraffinic solvent based paints, said resin being comprised of repeat units which are derived from (a) about 5 to about 60 weight percent tertiary-butyl cyclohexyl methacrylate, (b) 0 to about 40 weight percent vinyl aromatic monomers, (c) about 20 to about 80 weight percent alkyl methacrylate monomers, and (d) about 1 to about 30 weight percent alkyl acrylate monomers.
The subject invention further discloses a paint formulation which is comprised of (a) a paraffinic solvent; (b) a resin which is comprised of repeat units which are derived from (i) about 5 to about 60 weight percent tertiary-butyl cyclohexyl methacrylate, (ii) 0 to about 40 weight percent vinyl aromatic monomers, (iii) about 20 to about 80 weight percent alkyl methacrylate monomers, and (iv) about 1 to about 30 weight percent alkyl acrylate monomers; and (c) one or more pigments.
The paint resins of this invention are synthesized utilizing free radical emulsion polymerization techniques. This is carried out by adding a tertiary-butyl cyclohexyl methacrylate (TBCHMA), optionally vinyl aromatic monomers, an alkyl methacrylate monomer, and an alkyl acrylate monomer to water to form an aqueous polymerization medium. The aqueous polymerization medium will also normally contain a required amount of a surfactant. Polymerization of the monomers is then initiated with a free radical generator to produce a latex of the resin. The latex made is subsequently coagulated to recover the resin.
In synthesizing the resins of this invention generally from about 5 weight percent to about 60 weight percent TBCHMA, from about 20 weight percent to about 80 weight percent alkyl methacrylate monomers, from about 2 weight percent to about 30 weight percent alkyl acrylate monomers, and from 0 to about 40 weight percent vinyl aromatic monomers are polymerized. It is generally preferred to limit the quantity of vinyl aromatic monomers in the resin since they normally lead to a reduced level of ultra-violet light resistance. For instance, vinyl aromatic monomers can be totally eliminated from the resin. In any case, these resins can be used in manufacturing paints for interior and exterior coatings.
In making resins for interior coatings normally from about 5 weight percent to about 40 weight percent TBCHMA, from about 25 weight percent to about 80 weight percent alkyl methacrylate monomers, from about 5 weight percent to about 25 weight percent alkyl acrylate monomers, and from 0 to about 40 weight percent vinyl aromatic monomers are polymerized. Resins for interior paints preferably contain from about 15 weight percent to about 35 weight percent TBCHMA, from about 30 weight percent to about 70 weight percent alkyl methacrylate monomers, from about 10 weight percent to about 25 weight percent alkyl acrylate monomers, and from 0 to about 35 weight percent vinyl aromatic monomers.
In making resins for exterior coatings normally from about 10 weight percent to about 60 weight percent TBCHMA, from about 30 weight percent to about 80 weight percent alkyl methacrylate monomers, from about 1 weight percent to about 20 weight percent alkyl acrylate monomers, and from 0 to about 15 weight percent vinyl aromatic monomers are polymerized. Resins for exterior paints preferably contain from about 10 weight percent to about 30 weight percent TBCHMA, from about 50 weight percent to about 80 weight percent alkyl methacrylate monomers, from about 2 weight percent to about 10 weight percent alkyl acrylate monomers, and from 0 to about 10 weight percent vinyl aromatic monomers.
The alkyl acrylate monomers that can be used in the resins of this invention generally have the structural formula: 
wherein R represents an alkyl group containing from 1 to 10 carbon atoms. The alkyl group in such alkyl acrylate monomers will preferably contain from 2 to 8 carbon atoms with alkyl groups that contain 8 carbon atoms being most preferred. Accordingly, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, and 2-ethyl hexyl acrylate are preferred alkyl acrylate monomers with 2-ethylhexyl acrylate being the most preferred. The alkyl groups in such alkyl acrylate monomers can be straight chained or branched. Thus, normal-propyl acrylate, isopropyl acrylate, normal-butyl acrylate, or tertiary-butyl acrylate can be employed.
The vinyl aromatic monomers which can optionally be included include all of those which are known to polymerize in free radical systems. Such vinyl aromatic monomers typically contain from 8 to 20 carbon atoms. Usually, the vinyl aromatic monomer will contain from 8 to 14 carbon atoms. Some representative examples of vinyl aromatic monomers that can be utilized include styrene, 1-vinyl napthalene, 2-vinyl napthalene, 3-methyl styrene, 4-propyl styrene, 4-cyclohexyl styrene, 4-dodecyl styrene, 2-ethyl-4-benzyl styrene, 4-(phenylbutyl) styrene, para-tertiary-butyl styrene, and the like. Styrene, para-methyl styrene, and mixtures of para-methyl styrene and ortho-methyl styrene are generally the most preferred vinyl aromatic monomers.
The alkyl methacrylate monomers that can be used have the structural formula: 
wherein R represents an alkyl group containing from 1 to 10 carbon atoms (Rxe2x95x90CnH2n+1 with n being an integer from 1 to 8). The alkyl groups in such alkyl methacrylate monomers can be straight chained or branched. Methyl methacrylate, ethyl methacrylate, propyl methacrylate, isobutyl methacrylate, and n-butyl methacrylate are representative examples of alkyl methacrylate monomers that can be used. The alkyl group in the alkyl methacrylate monomer will preferably contain from 1 to 4 carbon atoms with alkyl groups which contain 4 carbon atoms being most preferred. Accordingly, isobutyl methacrylate is a highly preferred monomer.
Essentially any type of free radical generator can be used to initiate such free radical emulsion polymerizations. For example, free radical generating chemical compounds, ultra-violet light or radiation can be used. In order to ensure a satisfactory polymerization rate, uniformity, and a controllable polymerization, free radical generating chemical agents which are water soluble under the polymerization conditions are generally used with good results.
Some representative examples of free radical initiators which are commonly used include the various peroxygen compounds such as potassium persulfate, ammonium persulfate, benzoyl peroxide, hydrogen peroxide, di-t-butyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, decanoyl peroxide, lauryl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, t-butyl hydroperoxide, acetyl acetone peroxide, dicetyl peroxydicarbonate, t-butyl peroxyacetate, t-butyl peroxymaleic acid, t-butyl peroxybenzoate, acetyl cyclohexyl sulfonyl peroxide, and the like; the various azo compounds such as 2-t-butylazo-2-cyanopropane, dimethyl azodiisobutyrate, 4,4xe2x80x2-azobis(4-cyanovaleric acid), azo carboxy valeric acid, azodiisobutyronitrile, 2-t-butylazo-1-cyanocyclohexane, 1-t-amylazo-1-cyanocyclohexane, and the like; the various alkyl perketals, such as 2,2-bis-(t-butylperoxy)butane, ethyl 3,3-bis (t-butylperoxy)butyrate, 1,1-di-(t-butylperoxy) cyclohexane, and the like. Persulfate initiators, such as potassium persulfate and ammonium persulfate are especially useful in such aqueous emulsion polymerizations.
The amount of initiator employed will vary with the desired molecular weight of the resin being synthesized. Higher molecular weights are achieved by utilizing smaller quantities of the initiator and lower molecular weights are attained by employing larger quantities of the initiator. However, as a general rule from 0.005 to 1 phm (parts by weight per 100 parts by weight of monomer) of the initiator will be included in the reaction mixture. In the case of metal persulfate initiators most commonly from 0.1 to 0.5 phm will be employed in the polymerization medium.
The emulsifiers used in the polymerizations of this invention may be charged at the outset of the polymerization or may be added incrementally or proportionately as the polymerization reaction proceeds. A wide variety of types of emulsifiers or surfactants, such as anionic, cationic, nonionic and amphoteric emulsifiers, can be utilized in the process of this invention. Rosin acid or fatty acid emulsifiers are normally utilized.
Synthetic surfactants can also be used. For instance, salts of alkyl sulfates, alkyl sulfonates and alkyl phosphates can be employed as the emulsifier. The alkyl groups in these compounds generally contain from 1 to 30 carbon atoms. Normally the alkyl groups in these surfactants will contain from 8 to 20 carbon atoms. The surfactant utilized will normally be a sodium, potassium, magnesium or ammonium salt. Sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecyl benzene sulfonate, and sodium dodecyl sulfate are some representative examples of highly suitable emulsifiers.
Generally from about 1.5 phm to about 8 phm of emulsifier is utilized in preparing the aqueous polymerization medium. In most cases, it will be preferred to utilize from about 4 phm to 6.5 phm of emulsifier. It is normally more preferred to utilize from about 5.5 phm to about 6.5 phm of the emulsifier. The precise amount of emulsifier required in order to attain optimal results will, of course, vary with the specific emulsifier being used. However, persons skilled in the art will be able to easily ascertain the specific amount of emulsifier required in order to attain optimal results.
The free radical emulsion polymerization will typically be conducted at a temperature that is within the range of about 20xc2x0 C. to about 95xc2x0 C. It is generally preferred for the polymerization to be carried out at a temperature that is within the range of 30xc2x0 C. to about 80xc2x0 C. It is typically more preferred to utilize a polymerization temperature that is within the range of about 45xc2x0 C. to about 70xc2x0 C. To increase conversion levels, it can be advantageous to increase the temperature as the polymerization proceeds. For instance, it is desirable for the polymerization temperature could be maintained at about 45xc2x0 C. at the beginning of the polymerization and increased to a final temperature of about 70xc2x0 C. at the end of the polymerization. After the polymerization has been completed the resin can be recovered from the latex by using standard coagulation and drying techniques.
The resins of this invention can be employed in manufacturing paraffinic solvent based paints. These paints utilize organic solvents that contain virtually no aromatic compounds. For instance, the paraffinic solvents employed in making the paints of this invention will normally contain less than about 2 weight percent aromatic compounds. It is normally preferred for the organic solvent used in making such paints to contain less than about 1 percent aromatic compounds.
The paints of this invention are comprised of the paraffinic solvent, the resin, and one or more pigments. Such paints can optionally contain fillers, plasticizers, stabilizers, dryers, fungicides, insecticides, antifouling agents, and anticorrosive agents.
Pigments are normally added to paint formulations to impart color and hiding power to the coating. Titanium dioxide is an example of a widely used pigment that imparts hiding power and a white color. Mineral pigments, such as oxides of iron and chromium, organic pigments, such as phthalocyanine, and active anticorrosive pigments, such as zinc phosphate, are representative examples of other widely used pigments.
Fillers are normally inexpensive materials that are added to the paint formulation to attain the desired consistency and non-settling characteristics. Fillers can also improve a coatings physical properties, such as resistance to cracking and abrasion. Some representative examples of widely utilized fillers include chalks, calcium carbonates, clays, micas, forms of barites and talcs, and silica.
Driers are chemical compounds, such as salts of cobalt, lead, manganese, barium, and zinc, which speed up drying. Plasticizers are agents which control the hardness of the film or which impart flexibility. Stabilizers are chemical agents that neutralize the destructive effects of heat and ultraviolet light. Fungicides and insecticides are commonly added to interior and exterior house paints. Antifouling compounds are commonly added to marine paints to inhibit marine growth.
This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, all parts and percentages are given by weight.